Subpicture tracks in coded video

ABSTRACT

Systems, methods and apparatus for processing visual media data are described. One example method includes performing a conversion between visual media data and a visual media file that includes one or more tracks that store one or more bitstreams of the visual media data; and wherein the visual media data comprises one or more pictures comprising one or more subpictures or one or more slices; wherein the visual media file stores the one or more tracks according to a format rule; and wherein the format rule specifies that a track that includes a sequence of the one or more slices or the one or more subpictures covers a rectangular area of the one or more pictures.

CROSS REFERENCE TO RELATED APPLICATIONS

Under the applicable patent law and/or rules pursuant to the Paris Convention, this application is made to timely claims the priority to and benefits of U.S. Provisional Patent Application No. 63/079,933, filed on Sep. 17, 2020, and U.S. Provisional Patent Application No. 63/088,126, filed on Oct. 6, 2020. For all purposes under the law, the entire disclosures of the aforementioned applications are incorporated by reference as part of the disclosure of this application.

TECHNICAL FIELD

This patent document relates to generation, storage and consumption of digital audio video media information in a file format.

BACKGROUND

Digital video accounts for the largest bandwidth use on the internet and other digital communication networks. As the number of connected user devices capable of receiving and displaying video increases, it is expected that the bandwidth demand for digital video usage will continue to grow.

SUMMARY

The present document discloses techniques that can be used by video encoders and decoders for processing coded representation of a video or an image according to a file format.

In one example aspect, a method for processing visual media data is disclosed. The method includes performing a conversion between visual media data and a visual media file that includes one or more tracks that store one or more bitstreams of the visual media data; and wherein the visual media data comprises one or more pictures comprising one or more subpictures or one or more slices; wherein the visual media file stores the one or more tracks according to a format rule; and wherein the format rule specifies that a track that includes a sequence of the one or more slices or the one or more subpictures covers a rectangular area of the one or more pictures.

In another example aspect, a method for processing visual media data is provided. The method includes performing a conversion between visual media data and a visual media file that includes one or more tracks that store one or more bitstreams of the visual media data according to a format rule; wherein the visual media file includes a base track that references one or more subpicture tracks that store coded information for one or more subpictures of the visual media data, and wherein the format rule specifies a process used to reconstruct a video unit from a sample in the base track and the one or more subpicture tracks.

In yet another example aspect, a video processing apparatus is disclosed. The video processing apparatus comprises a processor configured to implement above-described methods.

In yet another example aspect, a method of storing visual media data to a file including one or more bitstreams is disclosed. The method corresponds to above-described methods and further includes storing the one or more bitstream to a non-transitory computer-readable recording medium.

In yet another example aspect, a computer readable medium that stores a bitstream is disclosed. The bitstream is generated according to above-described methods.

In yet another example aspect, a video processing apparatus for storing a bitstream is disclosed, wherein the video processing apparatus is configured to implement above-described methods.

In yet another example aspect, a computer readable medium on which a bitstream complies to a file format that is generated according to above-described methods is disclosed.

These, and other, features are described throughout the present document.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of an example video processing system.

FIG. 2 is a block diagram of a video processing apparatus.

FIG. 3 is a flowchart for an example method of video processing.

FIG. 4 is a block diagram that illustrates a video coding system in accordance with some embodiments of the present disclosure.

FIG. 5 is a block diagram that illustrates an encoder in accordance with some embodiments of the present disclosure.

FIG. 6 is a block diagram that illustrates a decoder in accordance with some embodiments of the present disclosure.

FIG. 7 shows an example of encoder block diagram.

FIG. 8 shows a picture partitioned into 18 tiles, 24 slices and 24 subpictures.

FIG. 9 A typical subpicture-based viewport-dependent 360° video delivery scheme.

FIG. 10 shows an example of extraction of one subpicture from a bitstream containing two subpictures and four slices.

FIGS. 11 and 12 show example methods of processing visual media data based on some implementations of the disclosed technology.

DETAILED DESCRIPTION

Section headings are used in the present document for ease of understanding and do not limit the applicability of techniques and embodiments disclosed in each section only to that section. Furthermore, H.266 terminology is used in some description only for ease of understanding and not for limiting scope of the disclosed techniques. As such, the techniques described herein are applicable to other video codec protocols and designs also. In the present document, editing changes are shown to text by strikethrough indicating cancelled text and highlight indicating added text (including boldface italic), with respect to the current draft of the VVC specification or ISOBMFF file format specification.

1. Initial Discussion

This document is related to video file format. Specifically, it is related to carriage of subpictures of a Versatile Video Coding (VVC) video bitstream in multiple tracks in a media file based on the ISO base media file format (ISOBMFF). The ideas may be applied individually or in various combination, for video bitstreams coded by any codec, e.g., the VVC standard, and for any video file format, e.g., the VVC video file format being developed.

2. Abbreviations

-   -   ACT adaptive colour transform     -   ALF adaptive loop filter     -   AMVR adaptive motion vector resolution     -   APS adaptation parameter set     -   AU access unit     -   AUD access unit delimiter     -   AVC advanced video coding (Rec. ITU-T H.264|ISO/IEC 14496-10)     -   B bi-predictive     -   BCW bi-prediction with CU-level weights     -   BDOF bi-directional optical flow     -   BDPCM block-based delta pulse code modulation     -   BP buffering period     -   CABAC context-based adaptive binary arithmetic coding     -   CB coding block     -   CBR constant bit rate     -   CCALF cross-component adaptive loop filter     -   CPB coded picture buffer     -   CRA clean random access     -   CRC cyclic redundancy check     -   CTB coding tree block     -   CTU coding tree unit     -   CU coding unit     -   CVS coded video sequence     -   DPB decoded picture buffer     -   DCI decoding capability information     -   DRAP dependent random access point     -   DU decoding unit     -   DUI decoding unit information     -   EG exponential-Golomb     -   EGk k-th order exponential-Golomb     -   EOB end of bitstream     -   EOS end of sequence     -   FD filler data     -   FIFO first-in, first-out     -   FL fixed-length     -   GBR green, blue, and red     -   GCI general constraints information     -   GDR gradual decoding refresh     -   GPM geometric partitioning mode     -   HEVC high efficiency video coding (Rec. ITU-T H.265|ISO/IEC         23008-2)     -   HRD hypothetical reference decoder     -   HSS hypothetical stream scheduler     -   I intra     -   IBC intra block copy     -   IDR instantaneous decoding refresh     -   ILRP inter-layer reference picture     -   IRAP intra random access point     -   LFNST low frequency non-separable transform     -   LPS least probable symbol     -   LSB least significant bit     -   LTRP long-term reference picture     -   LMCS luma mapping with chroma scaling     -   MIP matrix-based intra prediction     -   MPS most probable symbol     -   MSB most significant bit     -   MTS multiple transform selection     -   MVP motion vector prediction     -   NAL network abstraction layer     -   OLS output layer set     -   OP operation point     -   OPI operating point information     -   P predictive     -   PH picture header     -   POC picture order count     -   PPS picture parameter set     -   PROF prediction refinement with optical flow     -   PT picture timing     -   PU picture unit     -   QP quantization parameter     -   RADL random access decodable leading (picture)     -   RASL random access skipped leading (picture)     -   RBSP raw byte sequence payload     -   RGB red, green, and blue     -   RPL reference picture list     -   SAO sample adaptive offset     -   SAR sample aspect ratio     -   SEI supplemental enhancement information     -   SH slice header     -   SLI subpicture level information     -   SODB string of data bits     -   SPS sequence parameter set     -   STRP short-term reference picture     -   STSA step-wise temporal sublayer access     -   TR truncated rice     -   VBR variable bit rate     -   VCL video coding layer     -   VPS video parameter set     -   VSEI versatile supplemental enhancement information (Rec. ITU-T         H.274|ISO/IEC 23002-7)     -   VUI video usability information     -   VVC versatile video coding (Rec. ITU-T H.266|ISO/IEC 23090-3)

3. Video Coding Introduction

3.1. Video Coding Standards

Video coding standards have evolved primarily through the development of the well-known ITU-T and ISO/IEC standards. The ITU-T produced H.261 and H.263, ISO/IEC produced MPEG-1 and MPEG-4 Visual, and the two organizations jointly produced the H.262/MPEG-2 Video and H.264/MPEG-4 Advanced Video Coding (AVC) and H.265/HEVC standards. Since H.262, the video coding standards are based on the hybrid video coding structure wherein temporal prediction plus transform coding are utilized. To explore the future video coding technologies beyond HEVC, the Joint Video Exploration Team (JVET) was founded by VCEG and MPEG jointly in 2015. Since then, many new methods have been adopted by JVET and put into the reference software named Joint Exploration Model (JEM). The JVET was later renamed to be the Joint Video Experts Team (JVET) when the Versatile Video Coding (VVC) project officially started. VVC is the new coding standard, targeting at 50% bitrate reduction as compared to HEVC, that has been finalized by the JVET at its 19th meeting ended at Jul. 1, 2020.

The Versatile Video Coding (VVC) standard (ITU-T H.266|ISO/IEC 23090-3) and the associated Versatile Supplemental Enhancement Information (VSEI) standard (ITU-T H.274|ISO/IEC 23002-7) have been designed for use in a maximally broad range of applications, including both the traditional uses such as television broadcast, video conferencing, or playback from storage media, and also newer and more advanced use cases such as adaptive bit rate streaming, video region extraction, composition and merging of content from multiple coded video bitstreams, multiview video, scalable layered coding, and viewport-adaptive 360° immersive media.

3.2. File Format Standards

Media streaming applications are typically based on the IP, TCP, and HTTP transport methods, and typically rely on a file format such as the ISO base media file format (ISOBMFF). One such streaming system is dynamic adaptive streaming over HTTP (DASH). For using a video format with ISOBMFF and DASH, a file format specification specific to the video format, such as the AVC file format and the HEVC file format in ISO/IEC 14496-15 (“Information technology—Coding of audio-visual objects—Part 15: Carriage of network abstraction layer (NAL) unit structured video in the ISO base media file format”), would be needed for encapsulation of the video content in ISOBMFF tracks and in DASH representations and segments. Important information about the video bitstreams, e.g., the profile, tier, and level, and many others, would need to be exposed as file format level metadata and/or DASH media presentation description (MPD) for content selection purposes, e.g., for selection of appropriate media segments both for initialization at the beginning of a streaming session and for stream adaptation during the streaming session.

Similarly, for using an image format with ISOBMFF, a file format specification specific to the image format, such as the AVC image file format and the HEVC image file format in ISO/IEC 23008-12 (“Information technology—High efficiency coding and media delivery in heterogeneous environments—Part 12: Image File Format”), would be needed.

The VVC video file format, the file format for storage of VVC video content based on ISOBMFF, is currently being developed by MPEG. The latest draft specification of the VVC video file format is included in MPEG output document N19454 (“Information technology—Coding of audio-visual objects—Part 15: Carriage of network abstraction layer (NAL) unit structured video in the ISO base media file format—Amendment 2: Carriage of VVC and EVC in ISOBMFF”, July 2020).

The VVC image file format, the file format for storage of image content coded using VVC, based on ISOBMFF, is currently being developed by MPEG. The latest draft specification of the VVC image file format is included in MPEG output document N19460 (“Information technology—High efficiency coding and media delivery in heterogeneous environments—Part 12: Image File Format—Amendment 3: Support for VVC, EVC, slideshows and other improvements”, July 2020).

3.3. Picture Partitioning Schemes in HEVC

HEVC includes four different picture partitioning schemes, namely regular slices, dependent slices, tiles, and Wavefront Parallel Processing (WPP), which may be applied for Maximum Transfer Unit (MTU) size matching, parallel processing, and reduced end-to-end delay.

Regular slices are similar as in H.264/AVC. Each regular slice is encapsulated in its own NAL unit, and in-picture prediction (intra sample prediction, motion information prediction, coding mode prediction) and entropy coding dependency across slice boundaries are disabled. Thus a regular slice can be reconstructed independently from other regular slices within the same picture (though there may still have interdependencies due to loop filtering operations).

The regular slice is the only tool that can be used for parallelization that is also available, in virtually identical form, in H.264/AVC. Regular slices based parallelization does not require much inter-processor or inter-core communication (except for inter-processor or inter-core data sharing for motion compensation when decoding a predictively coded picture, which is typically much heavier than inter-processor or inter-core data sharing due to in-picture prediction). However, for the same reason, the use of regular slices can incur substantial coding overhead due to the bit cost of the slice header and due to the lack of prediction across the slice boundaries. Further, regular slices (in contrast to the other tools mentioned below) also serve as the key mechanism for bitstream partitioning to match MTU size requirements, due to the in-picture independence of regular slices and that each regular slice is encapsulated in its own NAL unit. In many cases, the goal of parallelization and the goal of MTU size matching place contradicting demands to the slice layout in a picture. The realization of this situation led to the development of the parallelization tools mentioned below.

Dependent slices have short slice headers and allow partitioning of the bitstream at treeblock boundaries without breaking any in-picture prediction. Basically, dependent slices provide fragmentation of regular slices into multiple NAL units, to provide reduced end-to-end delay by allowing a part of a regular slice to be sent out before the encoding of the entire regular slice is finished.

In WPP, the picture is partitioned into single rows of coding tree blocks (CTBs). Entropy decoding and prediction are allowed to use data from CTBs in other partitions. Parallel processing is possible through parallel decoding of CTB rows, where the start of the decoding of a CTB row is delayed by two CTBs, so to ensure that data related to a CTB above and to the right of the subject CTB is available before the subject CTB is being decoded. Using this staggered start (which appears like a wavefront when represented graphically), parallelization is possible with up to as many processors/cores as the picture contains CTB rows. Because in-picture prediction between neighboring treeblock rows within a picture is permitted, the required inter-processor/inter-core communication to enable in-picture prediction can be substantial. The WPP partitioning does not result in the production of additional NAL units compared to when it is not applied, thus WPP is not a tool for MTU size matching. However, if MTU size matching is required, regular slices can be used with WPP, with certain coding overhead.

Tiles define horizontal and vertical boundaries that partition a picture into tile columns and rows. Tile column runs from the top of a picture to the bottom of the picture. Likewise, tile row runs from the left of the picture to the right of the picture. The number of tiles in a picture can be derived simply as number of tile columns multiply by number of tile rows.

The scan order of CTBs is changed to be local within a tile (in the order of a CTB raster scan of a tile), before decoding the top-left CTB of the next tile in the order of tile raster scan of a picture. Similar to regular slices, tiles break in-picture prediction dependencies as well as entropy decoding dependencies. However, they do not need to be included into individual NAL units (same as WPP in this regard); hence tiles cannot be used for MTU size matching. Each tile can be processed by one processor/core, and the inter-processor/inter-core communication required for in-picture prediction between processing units decoding neighboring tiles is limited to conveying the shared slice header in cases a slice is spanning more than one tile, and loop filtering related sharing of reconstructed samples and metadata. When more than one tile or WPP segment is included in a slice, the entry point byte offset for each tile or WPP segment other than the first one in the slice is signaled in the slice header.

For simplicity, restrictions on the application of the four different picture partitioning schemes have been specified in HEVC. A given coded video sequence cannot include both tiles and wavefronts for most of the profiles specified in HEVC. For each slice and tile, either or both of the following conditions must be fulfilled: 1) all coded treeblocks in a slice belong to the same tile; 2) all coded treeblocks in a tile belong to the same slice. Finally, a wavefront segment contains exactly one CTB row, and when WPP is in use, if a slice starts within a CTB row, it must end in the same CTB row.

A recent amendment to HEVC is specified in the JCT-VC output document JCTVC-AC1005, J. Boyce, A. Ramasubramonian, R. Skupin, G. J. Sullivan, A. Tourapis, Y.-K. Wang (editors), “HEVC Additional Supplemental Enhancement Information (Draft 4),” Oct. 24, 2017, publicly available herein: http://phenix.int-evry.fr/jct/doc_end_user/documents/29_Macau/wg11/JCTVC-AC1005-v2.zip. With this amendment included, HEVC specifies three MCTS-related SEI messages, namely temporal MCTSs SEI message, MCTSs extraction information set SEI message, and MCTSs extraction information nesting SEI message.

The temporal MCTSs SEI message indicates existence of MCTSs in the bitstream and signals the MCTSs. For each MCTS, motion vectors are restricted to point to full-sample locations inside the MCTS and to fractional-sample locations that require only full-sample locations inside the MCTS for interpolation, and the usage of motion vector candidates for temporal motion vector prediction derived from blocks outside the MCTS is disallowed. This way, each MCTS may be independently decoded without the existence of tiles not included in the MCTS.

The MCTSs extraction information sets SEI message provides supplemental information that can be used in the MCTS sub-bitstream extraction (specified as part of the semantics of the SEI message) to generate a conforming bitstream for an MCTS set. The information consists of a number of extraction information sets, each defining a number of MCTS sets and containing RBSP bytes of the replacement VPSs, SPSs, and PPSs to be used during the MCTS sub-bitstream extraction process. When extracting a sub-bitstream according to the MCTS sub-bitstream extraction process, parameter sets (VPSs, SPSs, and PPSs) need to be rewritten or replaced, slice headers need to be slightly updated because one or all of the slice address related syntax elements (including first_slice_segment_in_pic_flag and slice_segment_address) typically would need to have different values.

3.4. Picture Partitioning and Subpictures in VVC

3.4.1. Picture Partitioning in VVC

In VVC, A picture is divided into one or more tile rows and one or more tile columns. A tile is a sequence of CTUs that covers a rectangular region of a picture. The CTUs in a tile are scanned in raster scan order within that tile.

A slice consists of an integer number of complete tiles or an integer number of consecutive complete CTU rows within a tile of a picture.

Two modes of slices are supported, namely the raster-scan slice mode and the rectangular slice mode. In the raster-scan slice mode, a slice contains a sequence of complete tiles in a tile raster scan of a picture. In the rectangular slice mode, a slice contains either a number of complete tiles that collectively form a rectangular region of the picture or a number of consecutive complete CTU rows of one tile that collectively form a rectangular region of the picture. Tiles within a rectangular slice are scanned in tile raster scan order within the rectangular region corresponding to that slice.

A subpicture contains one or more slices that collectively cover a rectangular region of a picture.

3.4.2. Subpicture Concept and Functionality

In VVC, each subpicture consists of one or more complete rectangular slices that collectively cover a rectangular region of the picture, e.g., as shown in FIG. 8 . A subpicture may be either specified to be extractable (i.e., coded independently of other subpictures of the same picture and of earlier pictures in decoding order) or not extractable. Regardless of whether a subpicture is extractable or not, the encoder can control whether in-loop filtering (including deblocking, SAO, and ALF) is applied across the subpicture boundaries individually for each subpicture.

Functionally, subpictures are similar to the motion-constrained tile sets (MCTSs) in HEVC. They both allow independent coding and extraction of a rectangular subset of a sequence of coded pictures, for use cases like viewport-dependent 360° video streaming optimization and region of interest (ROI) applications.

In streaming of 360° video, a.k.a. omnidirectional video, at any particular moment only a subset (i.e., the current viewport) of the entire omnidirectional video sphere would be rendered to the user, while the user can turn his/her head anytime to change the viewing orientation and consequently the current viewport. While it is desirable to have at least some lower-quality representation of the area not covered by the current viewport available at the client and ready to be rendered to the user just in case the user suddenly changes his/her viewing orientation to anywhere on the sphere, a high-quality representation of the omnidirectional video is only needed for the current viewport that is being rendered to the user at any given moment. Splitting the high-quality representation of the entire omnidirectional video into subpictures at an appropriate granularity enables such an optimization as shown in FIG. 8 with 12 high-resolution subpictures on the left-hand side and the remaining 12 subpictures of the omnidirectional video in lower resolution on the right-hand side.

Another typical subpicture-based viewport-dependent 360° video delivery scheme is shown in FIG. 9 , wherein only a higher-resolution representation of the full video consists of subpictures, while a lower-resolution representation of the full video does not use subpictures and can be coded with less frequent RAPs than the higher-resolution representation. The client receives the full video in the lower-resolution while for the higher-resolution video, the client only receives and decodes the subpictures that cover the current viewport.

3.4.3. Differences Between Subpictures and MCTSs

There are several important design differences between subpictures and MCTSs. First, the subpictures feature in VVC allows motion vectors of a coding block pointing outside of the subpicture even when the subpicture is extractable by applying sample padding at subpicture boundaries in this case, similarly as at picture boundaries. Second, additional changes were introduced for the selection and derivation of motion vectors in the merge mode and in the decoder side motion vector refinement process of VVC. This allows higher coding efficiency compared to the non-normative motion constraints applied at encoder-side for MCTSs. Third, rewriting of SHs (and PH NAL units, when present) is not needed when extracting of one or more extractable subpictures from a sequence of pictures to create a sub-bitstream that is a conforming bitstream. In sub-bitstream extractions based on HEVC MCTSs, rewriting of SHs is needed. Note that in both HEVC MCTSs extraction and VVC subpictures extraction, rewriting of SPSs and PPSs is needed. However, typically there are only a few parameter sets in a bitstream, while each picture has at least one slice, therefore rewriting of SHs can be a significant burden for application systems. Fourth, slices of different subpictures within a picture are allowed to have different NAL unit types. This is the feature often referred to as mixed NAL unit types or mixed subpicture types within a picture, discussed in more detail below. Fifth, VVC specifies HRD and level definitions for subpicture sequences, thus the conformance of the sub-bitstream of each extractable subpicture sequence can be ensured by encoders.

3.4.4. Mixed Subpicture Types within a Picture

In AVC and HEVC, all VCL NAL units in a picture need to have the same NAL unit type. VVC introduces the option to mix subpictures with certain different VCL NAL unit types within a picture, thus providing support for random access not only at the picture level but also at the subpicture level. In VVC VCL NAL units within a subpicture are still required to have the same NAL unit type.

The capability of random accessing from IRAP subpictures is beneficial for 360° video applications. In viewport-dependent 360° video delivery schemes similar to the one shown in FIG. 9 , the content of spatially neighboring viewports largely overlaps, i.e. only a fraction of subpictures in a viewport is replaced by new subpictures during a viewport orientation change, while most subpictures remain in the viewport. Subpicture sequences that are newly introduced into the viewport must begin with IRAP slices but significant reduction in overall transmission bit rate can be achieved when the remaining subpictures are allowed to carry out inter-prediction at viewport changes.

The indication of whether a picture contains just a single type of NAL units or more than one type is provided in the PPS referred to by the picture (i.e., using a flag called pps_mixed_nalu_types_in_pic_flag). A picture may consist of subpictures containing IRAP slices and subpictures containing trailing slices at the same time. A few other combinations of different NAL unit types within a picture are also allowed, including leading picture slices of NAL unit types RASL and RADL, which allows the merging of subpicture sequences with open-GOP and close-GOP coding structures extracted from different bitstreams into one bitstream.

3.4.5. Subpicture Layout and ID Signaling

The layout of subpictures in VVC is signaled in the SPS, thus constant within a CLVS. Each subpicture is signaled by the position of its top-left CTU and its width and height in number of CTUs, therefore ensuring that a subpicture covers a rectangular region of the picture with CTU granularity. The order in which the subpictures are signaled in the SPS determines the index of each subpicture within the picture.

For enabling extraction and merging of subpicture sequences without rewriting of SHs or PHs, the slice addressing scheme in VVC is based on subpicture IDs and a subpicture-specific slice index to associate slices to subpictures. In the SH, the subpicture ID of the subpicture containing the slice and the subpicture-level slice index are signaled. Note that the value of subpicture ID of a particular subpicture can be different from the value of its subpicture index. A mapping between the two is either signaled in the SPS or PPS (but never both) or implicitly inferred. When present, the subpicture ID mapping needs to be rewritten or added when rewriting the SPSs and PPSs during the subpicture sub-bitstream extraction process. The subpicture ID and the subpicture-level slice index together indicate to the decoder the exact position of the first decoded CTU of a slice within the DPB slot of the decoded picture. After sub-bitstream extraction, the subpicture ID of a subpicture remains unchanged while the subpicture index may change. Even when the raster-scan CTU address of the first CTU in a slice in the subpicture has changed compared to the value in the original bitstream, the unchanged values of subpicture ID and subpicture-level slice index in the respective SH would still correctly determine the position of each CTU in the decoded picture of the extracted sub-bitstream. FIG. 10 illustrates the usage of subpicture ID, subpicture index and subpicture-level slice index to enable subpicture extraction with an example containing two subpictures and four slices.

Similar to subpicture extraction, the signaling for subpictures allows merging several subpictures from different bitstreams into a single bitstream by only rewriting the SPSs and PPSs, provided that the different bitstreams are coordinately generated (e.g., using distinct subpicture IDs but otherwise mostly aligned SPS, PPS and PH parameters such as CTU size, chroma format, coding tools, etc.).

While subpictures and slices are independently signaled in the SPS and PPS, respectively, there are inherent reciprocal constraints between the subpicture and slice layouts in order to form a conformant bitstream. First, the presence of subpictures requires using rectangular slices and forbids raster-scan slices. Second, the slices of a given subpicture shall be consecutive NAL units in decoding order, which means that the subpicture layout constrains the order of coded slice NAL units within the bitstream.

3.5. Some Specifics of VVC Video File Format

3.5.1. Types of Tracks

The VVC video file format specifies the following types of video tracks for carriage of VVC bitstreams in ISOBMFF files:

a) VVC track:

-   -   A VVC track represents a VVC bitstream by including NAL units in         its samples and sample entries and possibly by referencing other         VVC tracks containing other sublayers of the VVC bitstream and         possibly by referencing VVC subpicture tracks. When a VVC track         references VVC subpicture tracks, it is referred to as a VVC         base track.         b) VVC non-VCL track:     -   APSs, which carry ALF, LMCS, or scaling list parameters, and         other non-VCL NAL units can be stored in and transmitted through         a track that is separate from the track containing the VCL NAL         units; this is the VVC non-VCL track.         c) VVC subpicture track:     -   A VVC subpicture track contains either of the following:         -   A sequence of one or more VVC subpictures.         -   A sequence of one or more complete slices forming a             rectangular area.     -   A sample of a VVC subpicture track contains either of the         following:         -   One or more complete subpictures as specified in ISO/IEC             23090-3 that are contiguous in decoding order.         -   One or more complete slices as specified in ISO/IEC 23090-3             that form a rectangular area and are contiguous in decoding             order.     -   The VVC subpictures or slices included in any sample of a VVC         subpicture track are contiguous in decoding order.         -   NOTE: VVC non-VCL tracks and VVC subpicture tracks enable an             optimal delivery of WC video in streaming applications as             follows. These tracks can each be carried in DASH             representations of their own, and for decoding and rendering             of a subset of the tracks, the DASH representations             containing the subset of the VVC subpicture tracks as well             as the DASH representation containing the non-VCL tracks can             be requested by the client, segment by segment. This way,             redundant transmission of APSs and other non-VCL NAL units             can be avoided.             3.5.2. Overview of Rectangular Regions Carried in a VVC             Bitstream             This document provides support for describing rectangular             regions composed of either:     -   A sequence of one or more VVC subpictures that are contiguous in         decoding order, or     -   A sequence of one or more complete slices that forms a         rectangular area and that are contiguous in decoding order.         A rectangular region covers a rectangle without holes.         Rectangular regions within a picture do not overlap with each         other.         Rectangular regions can be described through rectangular region         visual sample group description entries (i.e., instances of         RectangularRegionGroupEntry) with rect_region_flag equal to 1.         If each sample of a track consists of NAL units of only one         rectangular region, SampleToGroupBox of type ‘trif’ can be used         to associate samples to the rectangular region, but this         SampleToGroupBox of type ‘trif’ can be omitted if the default         sample grouping mechanism is used (i.e., when the version of the         SampleGroupDescriptionBox of type ‘trif’ is equal to or greater         than 2). Otherwise, samples, NAL units, and rectangular regions         are associated with each other through SampleToGroupBoxes of         type ‘nalm’ and grouping_type_parameter equal to ‘trif’ and         SampleGroupDescriptionBox of type ‘nalm’. A         RectangularRegionGroupEntry describes:     -   a rectangular region,     -   coding dependencies between this rectangular region and other         rectangular regions.         Each RectangularRegionGroupEntry is assigned a unique         identifier, called groupID. This identifier can be used to         associate NAL units in a sample to a particular         RectangularRegionGroupEntry.         Positioning and size of rectangular regions are identified using         luma sample coordinates.         When used with movie fragments, RectangularRegionGroupEntry can         be defined for the duration of the movie fragment, by defining a         new SampleGroupDescriptionBox in the track fragment box as         defined in clause 8.9.4 of ISO/IEC 14496-12. However, there         shall not be any RectangularRegionGroupEntry in a track fragment         that has the same groupID as a RectangularRegionGroupEntry         already defined.         The base region used in the RectangularRegionGroupEntry is the         picture to which the NAL units in a rectangular region         associated with this rectangular region group entry belongs.         If there is any change in the base region size in consecutive         samples (e.g. in case of reference picture resampling (RPR) or         SPS resize), samples should be associated with different         RectangularRegionGroupEntry entries reflecting their respective         base region size.         NAL units mapped to a rectangular region may either be carried         in a VVC track, as usual, or in a separate track called VVC         subpicture track.         3.5.3. Reconstructing a Picture Unit from a Sample in a VVC         Track Referencing VVC Subpicture Tracks         A sample of a VVC track is resolved to an access unit that         contains the following NAL units in the order of the bullets:     -   The AUD NAL unit, if any, when present (and the first NAL unit)         in the sample.     -   When the sample is the first sample of a sequence of samples         associated with the same sample entry, the parameter set and SEI         NAL units contained in the sample entry, if any.     -   The NAL units present in the sample up to and including the PH         NAL unit.     -   The content of the time-aligned (in decoding time) resolved         sample from each referenced VVC subpicture track in the order         specified in the ‘spor’ sample group description entry mapped to         this sample, excluding all VPS, DCI, SPS, PPS, AUD, PH, EOS, and         EOB NAL units, if any. The track references are resolved as         specified below.     -   NOTE 1: If the referenced VVC subpicture track is associated         with a VVC non-VCL track, the resolved sample of the VVC         subpicture track contains the non-VCL NAL unit(s), if any, of         the time-aligned sample in the VVC non-VCL track.     -   The NAL units that follow the PH NAL unit in the sample.     -   NOTE 2: The NAL units that follow the PH NAL unit in the sample         could include suffix SEI NAL units, suffix APS NAL units, an EOS         NAL unit, an EOB NAL unit, or reserved NAL units that are         allowed after the last VCL NAL unit.         The ‘subp’ track reference indices of a ‘spor’ sample group         description entry are resolved as follows:     -   If the track reference points to a track ID of a VVC subpicture         track, the track reference is resolved to the VVC subpicture         track.     -   Otherwise (the track reference points to an ‘alte’ track group),         the track reference is resolved to any of the tracks of the         ‘alte’ track group. If a particular track reference index value         was resolved to a particular track in the previous sample, it         shall be resolved in the current sample to either of the         following:         -   the same particular track, or         -   any other track in the same ‘alte’ track group that contains             a sync sample that is time-aligned with the current sample.     -   NOTE 3: The VVC subpicture tracks in the same ‘alte’ track group         are necessarily independent of any other VVC subpicture tracks         referenced by the same VVC base track to avoid decoding         mismatches and could therefore be constrained as follows:         -   All the VVC subpicture tracks contain VVC subpictures.         -   The subpicture boundaries are like picture boundaries.         -   Loop filtering is turned off across subpicture boundaries.             If a reader selects VVC subpicture tracks containing VVC             subpictures with a set of subpicture ID values that is the             initial selection or differs from the previous selection,             the following steps may be taken:     -   The ‘spor’ sample group description entry is studied to conclude         whether a PPS or SPS NAL unit needs to be changed.     -   NOTE: An SPS change is only possible at the start of a CLVS.     -   If the ‘spor’ sample group description entry indicates that         start code emulation prevention bytes are present before or         within the subpicture IDs in the containing NAL unit, an RBSP is         derived from the NAL unit (i.e., start code emulation prevention         bytes are removed). After the overriding in the next step, start         code emulation prevention is re-done.     -   The reader uses the bit position and subpicture ID length         information in the ‘spor’ sample group entry to conclude which         bits are overwritten to update the subpicture IDs to the         selected ones.     -   When the subpicture ID values of a PPS or SPS are initially         selected, the reader needs to rewrite the PPS or SPS,         respectively, with the selected subpicture ID values in the         reconstructed access unit.     -   When the subpicture ID values of a PPS or SPS are changed         compared to the previous PPS or SPS (respectively) with the same         PPS ID value or SPS ID value (respectively), the reader needs to         include a copy of that previous PPS and SPS (if the PPS or SPS         with that same PPS or SPS ID value, respectively, is not present         in the access unit otherwise) and rewrite the PPS or SPS         (respectively) with the updated subpicture ID values in the         reconstructed access unit.         3.5.4. Subpicture Order Sample Group         3.5.4.1. Definition         This sample group is used in VVC base tracks, i.e., in VVC         tracks with ‘ subp’ track referencing to VVC subpicture tracks.         Each sample group description entry indicates the subpictures or         slices of a coded picture in decoding order, where each index of         the track reference of type ‘ subp’ indicates one or more         subpictures or slices that are contiguous in decoding order.         To ease PPS or SPS rewriting in response to subpicture         selection, each sample group description entry may contain:     -   an indication of whether selected subpicture IDs should be         changed in PPS or SPS NAL units;     -   the length (in bits) of subpicture ID syntax elements;     -   the bit position of subpicture ID syntax elements in the         containing RBSP;     -   a flag indicating whether start code emulation prevention bytes         are present before or within subpicture IDs;     -   the parameter set ID of the parameter set containing the         subpicture IDs.         3.5.4.2. Syntax

aligned (8) class VvcSubpicOrderEntry( ) extends VisualSampleGroupEntry(‘spor’) {  unsigned int (1) subpic_id_info_flag;  unsigned int (15) num_subpic_ref_idx;  for (i = 0; i < num_subpic_ref_idx; i++)   unsigned int (16) subp_track_ref_idx;  if (subpic_id_info_flag) {   unsigned int (4) subpic_id_len_minus1;   unsigned int (12) subpic_id_bit_pos;   unsigned int (1) start_code_emul_flag;   unsigned int (1) pps_subpic_id_flag;   if (pps_subpic_id_flag)    unsigned int (6) pps_id;   else {    unsigned int (1) sps_subpic_id_flag;    unsigned int (4) sps_id;    bit (1) reserved = 0;   }  } } 3.5.4.3. Semantics

-   -   subpic_id_info_flag equal to 0 specifies that the subpicture ID         values provided in the SPSs and/or PPSs are correct for the         indicated set of subp_track_ref_idx values and thus no rewriting         of SPSs or PPSs is required. subpic_info_flag equal to 1         specifies that SPSs and/or PPSs may need rewriting to indicate         the subpictures corresponding to the set of subp_track_ref_idx         values.     -   num_subpic_ref_idx specifies the number of reference indices of         subpicture tracks or track groups of subpicture tracks         referenced by the VVC track.     -   subp_track_ref_idx, for each value of i, specifies a ‘ subp’         track reference index of the i-th list of one or more         subpictures or slices to be included in the VVC bitstream         reconstructed from the VVC track.     -   subpic_id_len_minus1 plus 1 specifies the number of bits in         subpicture identifier syntax elements in PPS or SPS, whichever         is referenced by this structure.     -   subpic_id_bit_pos specifies the bit position starting from 0 of         the first bit of the first subpicture ID syntax element in the         referenced PPS or SPS RBSP.     -   start_code_emul_flag equal to 0 specifies that start code         emulation prevention bytes are not present before or within         subpicture IDs in the referenced PPS or SPS NAL unit.         start_code_emul_flag equal to 1 specifies that start code         emulation prevention bytes may be present before or within         subpicture IDs in the referenced PPS or SPS NAL unit.     -   pps_subpic_id_flag, when equal to 0, specifies that the PPS NAL         units applying to the samples mapped to this sample group         description entry do not contain subpicture ID syntax elements.         pps_subpic_id_flag, when equal to 1, specifies that the PPS NAL         units applying to the samples mapped to this sample group         description entry contain subpicture ID syntax elements.     -   pps_id, when present, specifies the PPS ID of the PPS applying         to the samples mapped to this sample group description entry.     -   sps_subpic_id_flag, when present and equal to 0, specifies that         the SPS NAL units applying to the samples mapped to this sample         group description entry do not contain subpicture ID syntax         elements and the subpicture ID values are inferred.         sps_subpic_id_flag, when present and equal to 1, specifies that         the SPS NAL units applying to the samples mapped to this sample         group description entry contain subpicture ID syntax elements.     -   sps_id, when present, specifies the SPS ID of the SPS applying         to the samples mapped to this sample group description entry.         3.5.5. Subpicture Entity Groups         3.5.5.1. General         Subpicture entity groups are defined providing level information         indicating conformance of a merged bitstream out of several VVC         subpicture tracks.     -   NOTE: VVC base tracks provides another mechanism for merging VVC         subpicture tracks.         Implicit reconstruction process requires modification of         parameter sets. The subpicture entity groups give guidance to         ease parameter set generation for the reconstructed bitstreams.         When the coded subpictures within the group that are to be         jointly decoded are interchangeable, i.e. the player selects a         number of active tracks from a group of sample-wise subpictures         with the same level contribution, the SubpicCommonGroupBox         indicates the combinatorial rules and the level_idc of a         resulting combination when decoded jointly.         When there are coded subpictures with different properties, e.g.         different resolution, which are selected to be jointly decoded,         the SubpicMultipleGroupsBox indicates the combinatorial rules         and the level_idc of a resulting combination when decoded         jointly.         All the entity_id values included in the subpicture entity         groups shall identify VVC subpicture tracks. When present,         SubpicCommonGroupBox and SubpicMultipleGroupsBox shall be         contained in the GroupsListBox in the movie-level MetaBox and         shall not be contained in file-level or track-level MetaBoxes.         3.5.5.2. Syntax of Subpicture Common Group Box

aligned (8) class SubpicCommonGroupBox extends EntityToGroupBox(‘acgl’, 0, 0) {  unsigned int (32) level_idc;  unsigned int (32) num_active_tracks; } 3.5.5.3. Semantics of Subpicture Common Group Box

-   -   level_idc specifies the level to which any selection of         num_active_tracks entities among the entity group conforms.     -   num_active_tracks specifies the number of tracks for which the         value of level_idc is provided.         3.5.5.4. Syntax of Subpicture Multiple Groups Box

aligned (8) class SubpicMultipleGroupsBox extends EntityToGroupBox(‘amgl’, 0, 0) {  unsigned int (32) level_idc;  unsigned int (32) num_subgroup_ids;  subgroupIdLen = (num_subgroup_ids >= (1 << 24)) ? 32 :   (num_subgroup_ids >= (1 << 16)) ? 24 :   (num_subgroup_ids >= (1 << 8)) ? 16 : 8;  for (i = 0; i < num_entities_in_group; i++)   unsigned int(subgroupIdLen) track_subgroup_id[i];  for (i = 0; i < num_subgroup_ids; i++)   unsigned int (32) num_active_tracks[i]; } 3.5.5.5. Semantics

-   -   level_idc specifies the level to which the combination of         selecting any num_active_tracks[i] tracks among the subgroup         with ID equal to i for all values of i in the range of 0 to         num_subgroup_ids−1, inclusive, conforms.     -   num_subgroup_ids specifies the number of separate subgroups,         each identified by the same value of track_subgroup_id[i].         Different subgroups are identified by different values of         track_subgroup_id[i].     -   track_subgroup_id [i] specifies the subgroup ID for the i-th         track in this entity group. subgroup ID values shall range from         0 to num_subgroup_ids−1, inclusive.     -   num_active_tracks [i] specifies the number of tracks among the         subgroup with ID equal to i that is documented in level_idc.

4. Example Technical Problems Addressed by Disclosed Technical Solutions

The latest designs of the VVC video file format regarding the carriage of subpictures in a VVC bitstreams in multiple tracks have the following problems:

-   -   1) A sample of a VVC subpicture track contains either of the         following: A) One or more complete subpictures as specified in         ISO/IEC 23090-3 that are contiguous in decoding order; B) One or         more complete slices as specified in ISO/IEC 23090-3 that form a         rectangular area and are contiguous in decoding order.         -   However, the following issue exists:             -   a. It would make more sense to also require a VVC                 subpicture track to cover a rectangular area when it                 contains subpictures, similarly as when it contains                 slices.             -   b. It would make more sense to require the subpictures                 or slices in a VVC subpicture track to be                 motion-constrained, i.e., extractable or self-contained.             -   c. Why not allow a VVC subpicture track to contain a set                 of subpictures that form a rectangular region but are                 not continuous in decoding order in the original                 bitstream but if this track itself is decoded then these                 subpictures are continuous in decoding order? Shouldn't                 that be allowed, e.g., for a field of view (FOV) of a                 360° video covered by some subpictures on the left and                 right boundaries of a projected picture?     -   2) In the reconstruction of a PU from a sample of a VVC base         track and the time-aligned samples in a list of VVC subpicture         tracks referenced by the VVC base track, the order of the         non-VCL NAL units in the sample of the VVC base track is not         clearly specified when the PH NAL unit is not present in the         sample.     -   3) The subpicture order sample group mechanism (‘spor’) enables         different order of the subpictures from the subpicture tracks in         the reconstructed bitstream for different samples, and enables         cases that need SPSs and/or PPS rewriting. However, it's not         clear why either of these flexibilities is needed. Therefore,         the ‘spor’ sample group mechanism is not needed and can be         removed.     -   4) In the reconstruction of a PU from a sample of a VVC base         track and the time-aligned samples in a list of VVC subpicture         tracks referenced by the VVC base track, when the NAL units in         the time-aligned sample of a VVC subpicture track are added to         the PU, all VPS, DCI, SPS, PPS, AUD, PH, EOS, and EOB NAL units,         if any, are excluded. However, what about OPI NAL units? What         about SEI NAL units? Why are these non-VCL NAL units allowed to         be present in the subpicture tracks? If there are present, is it         OK to just through them away in bitstream reconstruction?     -   5) The container of the boxes of the two subpicture entity         groups is specified as the movie-level MetaBox. However, only         when the boxes are contained in the file-level MetaBox can the         entity_id values of the entity group refer to track IDs.     -   6) The subpicture entity groups work for cases where the         relevant subpicture information is consistent throughout the         entire time duration of the tracks. However, this is not always         the case. For example, what if different CVSs have different         levels for a particular subpicture sequence? In that case,         sample groups should be used instead, to carry essentially the         same information, but allow certain information to differ for         different samples (e.g., CVSs).     -   7) A subpicture order (‘spor’) sample group is currently         mandated to be present in each VVC base track. The ‘spor’ sample         group mechanism enables different order of the subpictures from         the subpicture tracks in the reconstructed bitstream for         different samples, and enables cases that need SPSs and/or PPS         rewriting. However, in cases of straightforward “early-binding”         of subpictures through a ‘subp’ track reference in a VVC base         track, the ‘spor’ sample group is not needed.

5. A Listing of Technical Solutions

To solve the above problems, and others, methods as summarized below are disclosed. The inventions should be considered as examples to explain the general concepts and should not be interpreted in a narrow way. Furthermore, these inventions can be applied individually or combined in any manner.

-   -   1) One or more of the following items are proposed on VVC         subpicture tracks:         -   a. Require a VVC subpicture track to cover a rectangular             area when it contains subpictures.         -   b. Require the subpictures or slices in a VVC subpicture             track to be motion-constrained such that they can extracted,             decoded, and presented without the presence of any of the             subpictures or slices covering other areas.             -   i. Alternatively, allow the subpictures or slices in a                 VVC subpicture track to be dependent in motion                 compensation on the subpictures or slices covering other                 areas, and consequently they cannot extracted, decoded,                 and presented without the presence of any of the                 subpictures or slices covering other areas.         -   c. Allow a VVC subpicture track to contain a set of             subpictures or slices that form a rectangular region but are             not contiguous in decoding order in the original/entire VVC             bitstream.             -   This enables a field of view (FOV) of a 360° video                 covered by subpictures that are not contiguous in                 decoding order in the original/entire VVC bitstream,                 e.g., on the left and right boundaries of a projected                 picture, to be represented by a VVC subpicture track.         -   d. Require that the order of the subpictures or slices in             each sample of a VVC subpicture track shall be the same as             the order of them in the original/entire VVC bitstream.         -   e. Add an indication of whether the decoding order of the             subpictures or slices in each sample of a VVC subpicture             track is contiguous in the original/entire VVC bitstream.             -   i. This indication is, e.g., signalled in the VVC base                 track sample entry description, or somewhere else.             -   ii. Require that, when it is not indicated that the                 order of the subpictures or slices in each sample of a                 VVC subpicture track is contiguous in decoding order in                 the original/entire VVC bitstream, the subpictures or                 slices in the track shall not be merged with subpictures                 or slices in other VVC subpicture tracks. For example,                 in this case, it is disallowed to have a VVC based track                 referencing, through track reference of type ‘subp’,                 both this VVC subpicture track and another VVC                 subpicture track.         -   f. Add a flag, nalusInContiguousDecodingOrderFlag, into the             VvcNALUConfigBox. This flag equal to 1 indicates that the             NAL units in each samples are contiguous in decoding order             in the original entire bitstream, thus a VVC base track that             references this VVC subpicture track through a track             reference of type ‘subp’ may also refer to other VVC             subpicture tracks through the same track reference. The             value 0 indicates that NAL units in each samples may or may             not be contiguous in decoding order in the original entire             bitstream, thus a VVC base track that references this VVC             subpicture track through a track reference of type ‘subp’             may not refer to other VVC subpicture tracks through the             same track reference.     -   2) In the reconstruction of a PU from a sample of a VVC base         track and the time-aligned samples in a list of VVC subpicture         tracks referenced by the VVC base track through a track         reference, the order of the non-VCL NAL units in the sample of         the VVC base track is clearly specified regardless of whether         there is a PH NAL unit in the sample.         -   a. In one example, the set NAL units from the sample of the             VVC base track to be placed in the PU before the NAL units             in the VVC subpicture tracks is specified as follows: If             there is at least one NAL unit in the sample with             nal_unit_type equal to EOS_NUT, EOB_NUT, SUFFIX_APS_NUT,             SUFFIX_SEI_NUT, FD_NUT, RSV_NVCL_27, UNSPEC_30, or UNSPEC_31             (a NAL unit with such a NAL unit type cannot precede the             first VCL NAL unit in a picture unit), the NAL units in the             sample up to and excluding the first of these NAL units,             otherwise all NAL units in the sample.         -   b. In one example, the set NAL units from the sample of the             VVC base track to be placed in the PU after the NAL units in             the VVC subpicture tracks is specified as follows: All NAL             units in the sample with nal_unit_type equal to EOS_NUT,             EOB_NUT, SUFFIX_APS_NUT, SUFFIX_SEI_NUT, FD_NUT,             RSV_NVCL_27, UNSPEC_30, or UNSPEC_31.     -   3) Allow a VVC track to refer to multiple (subpicture) tracks by         using ‘subp’ track reference, and the order of reference         indicates the decoding order of the subpictures in a bitstream         reconstructed from the referenced VVC subpicture tracks.         -   a. In the reconstruction of a PU from a sample of a VVC base             track and the time-aligned samples in a list of VVC             subpicture tracks referenced by the VVC base track, the             samples of the reference subpicture tracks are processed in             the order of the VVC subpicture tracks being referenced in             the ‘subp’ track reference.     -   4) Disallow the presence of any AU-level or picture-level         non-VCL NAL units in subpicture tracks, including AUD, DCI, OPI,         VPS, SPS, PPS, PH, EOS, and EOB NAL units, and SEI NAL units         containing AU-level and picture-level SEI messages only. An         AU-level SEI message applies to one or more entire AUs. A         picture-level SEI message applies to one or more entire         pictures.         -   a. Furthermore, in the reconstruction of a PU from a sample             of a VVC base track and the time-aligned samples in a list             of VVC subpicture tracks referenced by the VVC base track,             all NAL units in the time-aligned sample of a VVC subpicture             track are added to the PU, without discarding certain             non-VCL NAL units.     -   5) In the reconstruction of a PU from a sample of a VVC base         track and the time-aligned samples in a list of VVC subpicture         tracks referenced by the VVC base track through a track         reference, remove the use of the ‘spor’ sample group, and remove         the description of the parameter sets rewriting process based on         the ‘spor’ sample group.     -   6) Remove the specification of the ‘spor’ sample group.     -   7) It is specified that each ‘subp’ track reference index shall         refer to either a track ID of a VVC subpicture track or a track         group ID of a group of VVC subpicture tracks, nothing else.     -   8) To solve problem 5, the container of the boxes of the two         subpicture entity groups is specified to be the file-level         MetaBox as follows: When present, SubpicCommonGroupBox and         SubpicMultipleGroupsBox shall be contained in the GroupsListBox         in the file-level MetaBox and shall not be contained in         MetaBoxes of other levels.     -   9) To solve problem 6, add two sample groups to carry similar         information as carried by the two the subpicture entity groups,         such that VVC file format would support cases where the relevant         subpicture information is not consistent throughout the entire         time duration of the tracks, e.g., when different CVSs have         different levels for a particular subpicture sequence.     -   10) To solve problem 7, one or more of the following items are         proposed:         -   a. A ‘spor’ sample group is specified to be optional for             each VVC base track.         -   b. In the reconstruction of a PU, when a ‘spor’ sample group             is not present in the VVC base track, the samples of the             referenced subpicture tracks are processed in the order of             the VVC subpicture tracks being referenced in the ‘subp’             track reference.

6. Embodiments

Below are some example embodiments for some of the invention aspects summarized above in Section 5, which can be applied to the standard specification for VVC video file format. The changed texts are based on the latest draft specification in MPEG output document N19454 (“Information technology—Coding of audio-visual objects—Part 15: Carriage of network abstraction layer (NAL) unit structured video in the ISO base media file format—Amendment 2: Carriage of VVC and EVC in ISOBMFF”, July 2020). Most relevant parts that have been added or modified are highlighted in bold and Italic, and some of the deleted parts are marked with double brackets (e.g., [[a]] denotes deletion of the character, ‘a’). There may be some other changes that are editorial in nature and thus not highlighted.

6.1. First Embodiment

This embodiment is for items 1a, 1b, and 1c.

6.1.1. Types of Tracks

This specification specifies the following types of video tracks for carriage of VVC bitstreams:

-   -   a) VVC track:         -   A VVC track represents a VVC bitstream by including NAL             units in its samples and/or sample entries, and possibly by             associating other VVC tracks containing other layers and/or             sublayers of the VVC bitstream through the ‘vopi’ and ‘linf’             sample groups or through the ‘opeg’ entity group, and             possibly by referencing VVC subpicture tracks.         -   When a VVC track references VVC subpicture tracks, it is             also referred to as a VVC base track. A VVC base track shall             not contain VCL NAL units and shall not be referred to by a             VVC track through a ‘vvcN’ track reference.     -   b) VVC non-VCL track:         -   A VVC non-VCL track is a track that contains only non-VCL             NAL units and is referred to by a VVC track through a ‘vvcN’             track reference.         -   A VVC non-VCL track may contain APSs, which carry ALF, LMCS,             or scaling list parameters, with or without other non-VCL             NAL units, stored in and transmitted through a track that is             separate from the track containing the VCL NAL units.         -   A VVC non-VCL trac may also contain picture header NAL             units, with or without APS NAL units, and with or without             other non-VCL NAL units, stored in and transmitted through a             track that is separate from the track containing the VCL NAL             units.     -   c) VVC subpicture track:         -   A VVC subpicture track contains either of the following:             -   A sequence of one or more VVC subpictures                 .             -   A sequence of one or more complete slices forming a                 rectangular area.         -   A sample of a VVC subpicture track contains either of the             following:             -   One or more complete subpictures as specified in ISO/IEC                 23090-3 that [[are contiguous in decoding order]]             -   One or more complete slices as specified in ISO/IEC                 23090-3 that form [[a]]                 rectangular                 [[area and are contiguous in decoding order]].         -   [[The VVC subpictures or slices included in any sample of a             VVC subpicture track are contiguous in decoding order.]]             -   NOTE: VVC non-VCL tracks and VVC subpicture tracks                 enable an optimal delivery of VVC video in streaming                 applications as follows. These tracks can each be                 carried in DASH representations of their own, and for                 decoding and rendering of a subset of the tracks, the                 DASH representations containing the subset of the VVC                 subpicture tracks as well as the DASH representation                 containing the non-VCL tracks can be requested by the                 client, segment by segment. This way, redundant                 transmission of APSs and other non-VCL NAL units can be                 avoided,                 6.1.2. Overview of Rectangular Regions Carried in a VVC                 Bitstream                 This document provides support for describing                 rectangular regions composed of either:     -   A sequence of one or more VVC subpictures that [[are contiguous         in decoding order]]         , or     -   A sequence of one or more complete slices that forms a         rectangular         [[area and that are contiguous in decoding order]].         A rectangular region covers a rectangle without holes.         Rectangular regions within a picture do not overlap with each         other.         . . .

6.2. Second Embodiment

This embodiment is for items 2, 2a, 2b, 3, 3a, 4, 4a, and 5.

6.2.1. Reconstructing a Picture Unit from a Sample in a VVC Track Referencing VVC Subpicture Tracks

A sample of a VVC track is resolved to [[an access unit]]

that contains the following NAL units in the order of the bullets:

-   -   The AUD NAL unit, [[if any,]] when present [[(and the first NAL         unit)]] in the sample.

    -   

    -   When the sample is the first sample of a sequence of samples         associated with the same sample entry, the parameter set and SEI         NAL units contained in the sample entry, if any.

    -   [[The NAL units present in the sample up to and including the PH         NAL unit]]

    -   The content of the time-aligned (in decoding time) resolved         sample from each referenced VVC subpicture track in the order         [[specified in the ‘spor’ sample group description entry mapped         to this sample, excluding all VPS, DCI, SPS, PPS, AUD, PH, EOS,         and EOB NAL units, if any]]. The track references are resolved         as specified below.

    -   NOTE 2: If a referenced VVC subpicture track is associated with         a WC non-VCL track, the resolved sample of the WC subpicture         track contains the non-VCL NAL unit(s), if any, of the         time-aligned sample in the WC non-VCL track.

    -   [[The NAL units that follow the PH NAL unit in the sample]]

    -   [[NOTE 2: The NAL units that follow the PH NAL unit in the         sample could include suffix SEI NAL units, suffix APS NAL units,         an EOS NAL unit, an EOB NAL unit, or reserved NAL units that are         allowed after the last VCL NAL unit.]]         The ‘subp’ track reference indices [[of a ‘spor’ sample group         description entry]] are resolved as follows:

    -   If the track reference points to a track ID of a VVC subpicture         track, the track reference is resolved to the VVC subpicture         track.

    -   Otherwise (the track reference points to an ‘alte’ track group),         the track reference is resolved to any of the tracks of the         ‘alte’ track group, and if a particular track reference index         value was resolved to a particular track in the previous sample,         it shall be resolved in the current sample to either of the         following:         -   the same particular track, or         -   any other track in the same ‘alte’ track group that contains             a sync sample that is time-aligned with the current sample.

    -   NOTE 3: The VVC subpicture tracks in the same ‘alte’ track group         are necessarily independent of any other VVC subpicture tracks         referenced by the same VVC base track to avoid decoding         mismatches and could therefore be constrained as follows:         -   All the VVC subpicture tracks contain VVC subpictures.         -   The subpicture boundaries are like picture boundaries.         -   [[Loop filtering is turned off across subpicture boundaries.             If a reader selects VVC subpicture tracks containing VVC             subpictures with a set of subpicture ID values that is the             initial selection or differs from the previous selection,             the following steps may be taken:

    -   The ‘spor’ sample group description entry is studied to conclude         whether a PPS or SPS NAL unit needs to be changed.

    -   NOTE: An SPS change is only possible at the start of a CLVS.

    -   If the ‘spor’ sample group description entry indicates that         start code emulation prevention bytes are present before or         within the subpicture IDs in the containing NAL unit, an RBSP is         derived from the NAL unit (i.e., start code emulation prevention         bytes are removed). After the overriding in the next step, start         code emulation prevention is re-done.

    -   The reader uses the bit position and subpicture ID length         information in the ‘spor’ sample group entry to conclude which         bits are overwritten to update the subpicture IDs to the         selected ones.

    -   When the subpicture ID values of a PPS or SPS are initially         selected, the reader needs to rewrite the PPS or SPS,         respectively, with the selected subpicture ID values in the         reconstructed access unit.

    -   When the subpicture ID values of a PPS or SPS are changed         compared to the previous PPS or SPS (respectively) with the same         PPS ID value or SPS ID value (respectively), the reader needs to         include a copy of that previous PPS and SPS (if the PPS or SPS         with that same PPS or SPS ID value, respectively, is not present         in the access unit otherwise) and rewrite the PPS or SPS         (respectively) with the updated subpicture ID values in the         reconstructed access unit.]]

6.3. Third Embodiment

This embodiment is for items 1a, 1b, 1c, 1f, 2, 2a, 2b, 4, 4a, 10.

Types of Tracks

This specification specifies the following types of video tracks for carriage of VVC bitstreams:

-   -   d) VVC track:         -   A VVC track represents a VVC bitstream by including NAL             units in its samples and/or sample entries, and possibly by             associating other VVC tracks containing other layers and/or             sublayers of the VVC bitstream through the ‘vopi’ and ‘linf’             sample groups or through the ‘opeg’ entity group, and             possibly by referencing VVC subpicture tracks.         -   When a VVC track references VVC subpicture tracks, it is             also referred to as a VVC base track.

    -   e) VVC non-VCL track:         -   A VVC non-VCL track is a track that contains only non-VCL             NAL units and is referred to by a VVC track through a ‘vvcN’             track reference.         -   A VVC non-VCL track may contain APSs, which carry ALF, LMCS,             or scaling list parameters, with or without other non-VCL             NAL units, stored in and transmitted through a track that is             separate from the track containing the VCL NAL units.         -   A VVC non-VCL trac may also contain picture header NAL             units, with or without APS NAL units, and with or without             other non-VCL NAL units, stored in and transmitted through a             track that is separate from the track containing the VCL NAL             units.

    -   f) VVC subpicture track:         -   A VVC subpicture track contains either of the following:             -   A sequence of one or more VVC subpictures             -   A sequence of one or more complete slices forming a                 rectangular area.         -   A sample of a VVC subpicture track contains either of the             following:             -   One or more complete subpictures as specified in ISO/IEC                 23090-3 that [[are contiguous in decoding order]]             -   One or more complete slices as specified in ISO/IEC                 23090-3 that form [[a]]                 rectangular                 [[area and are contiguous in decoding order]].         -   [[The VVC subpictures or slices included in any sample of a             VVC subpicture track are contiguous in decoding order.]]             -   NOTE: VVC non-VCL tracks and VVC subpicture tracks                 enable an optimal delivery of VVC video in streaming                 applications as follows. These tracks can each be                 carried in DASH representations of their own, and for                 decoding and rendering of a subset of the tracks, the                 DASH representations containing the subset of the VVC                 subpicture tracks as well as the DASH representation                 containing the non-VCL tracks can be requested by the                 client, segment by segment. This way, redundant                 transmission of APSs and other non-VCL NAL units can be                 avoided,                 Overview of rectangular regions carried in a VVC                 bitstream                 This document provides support for describing                 rectangular regions composed of either:

    -   A sequence of one or more VVC subpictures that [[are contiguous         in decoding order]]         or

    -   A sequence of one or more complete slices that forms a         rectangular         [[area and that are contiguous in decoding order]].         A rectangular region covers a rectangle without holes.         Rectangular regions within a picture do not overlap with each         other.         . . .         Reconstructing a picture unit from a sample in a VVC track         referencing VVC subpicture tracks A sample of a VVC track is         resolved to [[an access unit]]         that contains the following NAL units in the order of the         bullets:

    -   The AUD NAL unit, [[if any,]] when present [[(and the first NAL         unit)]] in the sample.

    -   

    -   When the sample is the first sample of a sequence of samples         associated with the same sample entry, the parameter set and SEI         NAL units contained in the sample entry, if any.

    -   [[The NAL units present in the sample up to and including the PH         NAL unit]]

    -   The content of the time-aligned (in decoding time) resolved         sample from each referenced VVC subpicture track in the order         specified in the ‘spor’ sample group description entry mapped to         this sample[[, excluding all VPS, DCI, SPS, PPS, AUD, PH, EOS,         and EOB NAL units, if any]]. The track references are resolved         as specified below.

    -   NOTE 2: If a referenced VVC subpicture track is associated with         a WC non-VCL track, the resolved sample of the WC subpicture         track contains the non-VCL NAL unit(s), if any, of the         time-aligned sample in the VVC non-VCL track.

    -   

    -   [[The NAL units that follow the PH NAL unit in the sample]]

    -   [[NOTE 2: The NAL units that follow the PH NAL unit in the         sample could include suffix SEI NAL units, suffix APS NAL units,         an EOS NAL unit, an EOB NAL unit, or reserved NAL units that are         allowed after the last VCL NAL unit.]]         The ‘subp’ track reference indices [[of a ‘spor’ sample group         description entry]] are resolved as follows:

    -   If the track reference points to a track ID of a VVC subpicture         track, the track reference is resolved to the VVC subpicture         track.

    -   Otherwise (the track reference points to an ‘alte’ track group),         the track reference is resolved to any of the tracks of the         ‘alte’ track group, and if a particular track reference index         value was resolved to a particular track in the previous sample,         it shall be resolved in the current sample to either of the         following:         -   the same particular track, or         -   any other track in the same ‘alte’ track group that contains             a sync sample that is time-aligned with the current sample.

    -   NOTE 3: The VVC subpicture tracks in the same ‘alte’ track group         are necessarily independent of any other VVC subpicture tracks         referenced by the same VVC base track to avoid decoding         mismatches and could therefore be constrained as follows:         -   All the VVC subpicture tracks contain VVC subpictures.         -   The subpicture boundaries are like picture boundaries.         -   [[Loop filtering is turned off across subpicture             boundaries.]]             If a reader selects VVC subpicture tracks containing VVC             subpictures with a set of subpicture ID values that is the             initial selection or differs from the previous selection,             the following steps may be taken:

    -   The ‘spor’ sample group description entry is studied to conclude         whether a PPS or SPS NAL unit needs to be changed.

    -   NOTE: An SPS change is only possible at the start of a CLVS.

    -   If the ‘spor’ sample group description entry indicates that         start code emulation prevention bytes are present before or         within the subpicture IDs in the containing NAL unit, an RBSP is         derived from the NAL unit (i.e., start code emulation prevention         bytes are removed). After the overriding in the next step, start         code emulation prevention is re-done.

    -   The reader uses the bit position and subpicture ID length         information in the ‘spor’ sample group entry to conclude which         bits are overwritten to update the subpicture IDs to the         selected ones.

    -   When the subpicture ID values of a PPS or SPS are initially         selected, the reader needs to rewrite the PPS or SPS,         respectively, with the selected subpicture ID values in the         reconstructed access unit.

    -   When the subpicture ID values of a PPS or SPS are changed         compared to the previous PPS or SPS (respectively) with the same         PPS ID value or SPS ID value (respectively), the reader needs to         include a copy of that previous PPS and SPS (if the PPS or SPS         with that same PPS or SPS ID value, respectively, is not present         in the access unit otherwise) and rewrite the PPS or SPS         (respectively) with [[with]] the updated subpicture ID values in         the reconstructed access unit.         Sample entry name and format (of VVC video stream definition)

Definition

. . .

A VVC track may contain a ‘subp’ track reference, with entries containing either a track_ID value of a VVC subpicture track or a track_group_id value of an ‘alte’ track group of VVC subpicture tracks.

[(When a VVC track contains a ‘subp’ track reference, it is referred to as a VVC base track and the following applies:

-   -   The samples of the VVC track shall not contain VCL NAL units]]     -   A sample group of type ‘spor’, as specified in clause 11.7.7,         [[shall]]         be present         .

. . . Syntax class VvcConfigurationBox extends Box(‘vvcC’) {  VvcDecoderConfigurationRecord( ) VvcConfig; } class VvcNALUConfigBox extends Box(‘vvnC’) {  unsigned int ([[6]]5) reserved=0;  

 

;  unsigned int (2) lengthSizeMinusOne; } class VvcSampleEntry( ) extends VisualSampleEntry (‘vvc1’ or ‘vvi1’){  VvcConfigurationBox config;  MPEG4ExtensionDescriptorsBox ( ); // optional } class VvcSubpicSampleEntry( ) extends VisualSampleEntry (‘vvs1’){  VvcNALUConfigBox config; } Semantics

-   -   Compressorname in the base class visualSampleEntry indicates the         name of the compressor used with the value “\ 012VVC Coding”         being recommended (\012 is 10, the length of the string in         bytes).

    -   VvcDecoderConfigurationRecord is defined in 11.3.3.

    -   

    -   lengthSizeMinusOne plus 1 indicates the length in bytes of the         NALUnitLength field in a track that contains the         VvcNALUConfigBox. The value of this field shall be one of 0, 1,         or 3 corresponding to a length encoded with 1, 2, or 4 bytes,         respectively.

    -   [[num_subpics_minus 1 plus 1 specifies the number of subpicture         sequences contained in the VVC subpicture track.

    -   subpic_id specifies the subpicture identifier of the sequence of         subpictures contained in the VVC subpicture track.]]

FIG. 1 is a block diagram showing an example video processing system 1900 in which various techniques disclosed herein may be implemented. Various implementations may include some or all of the components of the system 1900. The system 1900 may include input 1902 for receiving video content. The video content may be received in a raw or uncompressed format, e.g., 8 or 10 bit multi-component pixel values, or may be in a compressed or encoded format. The input 1902 may represent a network interface, a peripheral bus interface, or a storage interface. Examples of network interface include wired interfaces such as Ethernet, passive optical network (PON), etc. and wireless interfaces such as Wi-Fi or cellular interfaces.

The system 1900 may include a coding component 1904 that may implement the various coding or encoding methods described in the present document. The coding component 1904 may reduce the average bitrate of video from the input 1902 to the output of the coding component 1904 to produce a coded representation of the video. The coding techniques are therefore sometimes called video compression or video transcoding techniques. The output of the coding component 1904 may be either stored, or transmitted via a communication connected, as represented by the component 1906. The stored or communicated bitstream (or coded) representation of the video received at the input 1902 may be used by the component 1908 for generating pixel values or displayable video that is sent to a display interface 1910. The process of generating user-viewable video from the bitstream representation is sometimes called video decompression. Furthermore, while certain video processing operations are referred to as “coding” operations or tools, it will be appreciated that the coding tools or operations are used at an encoder and corresponding decoding tools or operations that reverse the results of the coding will be performed by a decoder.

Examples of a peripheral bus interface or a display interface may include universal serial bus (USB) or high definition multimedia interface (HDMI) or Displayport, and so on. Examples of storage interfaces include SATA (serial advanced technology attachment), PCI, IDE interface, and the like. The techniques described in the present document may be embodied in various electronic devices such as mobile phones, laptops, smartphones or other devices that are capable of performing digital data processing and/or video display.

FIG. 2 is a block diagram of a video processing apparatus 3600. The apparatus 3600 may be used to implement one or more of the methods described herein. The apparatus 3600 may be embodied in a smartphone, tablet, computer, Internet of Things (IoT) receiver, and so on. The apparatus 3600 may include one or more processors 3602, one or more memories 3604 and video processing hardware 3606. The processor(s) 3602 may be configured to implement one or more methods described in the present document. The memory (memories) 3604 may be used for storing data and code used for implementing the methods and techniques described herein. The video processing hardware 3606 may be used to implement, in hardware circuitry, some techniques described in the present document. In some embodiments, the video processing hardware 3606 may be at least partly included in the processor 3602, e.g., a graphics co-processor.

FIG. 4 is a block diagram that illustrates an example video coding system 100 that may utilize the techniques of this disclosure.

As shown in FIG. 4 , video coding system 100 may include a source device 110 and a destination device 120. Source device 110 generates encoded video data which may be referred to as a video encoding device. Destination device 120 may decode the encoded video data generated by source device 110 which may be referred to as a video decoding device.

Source device 110 may include a video source 112, a video encoder 114, and an input/output (I/O) interface 116.

Video source 112 may include a source such as a video capture device, an interface to receive video data from a video content provider, and/or a computer graphics system for generating video data, or a combination of such sources. The video data may comprise one or more pictures. Video encoder 114 encodes the video data from video source 112 to generate a bitstream. The bitstream may include a sequence of bits that form a coded representation of the video data. The bitstream may include coded pictures and associated data. The coded picture is a coded representation of a picture. The associated data may include sequence parameter sets, picture parameter sets, and other syntax structures. I/O interface 116 may include a modulator/demodulator (modem) and/or a transmitter. The encoded video data may be transmitted directly to destination device 120 via I/O interface 116 through network 130 a. The encoded video data may also be stored onto a storage medium/server 130 b for access by destination device 120.

Destination device 120 may include an I/O interface 126, a video decoder 124, and a display device 122.

I/O interface 126 may include a receiver and/or a modem. I/O interface 126 may acquire encoded video data from the source device 110 or the storage medium/server 130 b. Video decoder 124 may decode the encoded video data. Display device 122 may display the decoded video data to a user. Display device 122 may be integrated with the destination device 120, or may be external to destination device 120 which be configured to interface with an external display device.

Video encoder 114 and video decoder 124 may operate according to a video compression standard, such as the High Efficiency Video Coding (HEVC) standard, Versatile Video Coding (VVM) standard and other current and/or further standards.

FIG. 5 is a block diagram illustrating an example of video encoder 200, which may be video encoder 114 in the system 100 illustrated in FIG. 4 .

Video encoder 200 may be configured to perform any or all of the techniques of this disclosure. In the example of FIG. 5 , video encoder 200 includes a plurality of functional components. The techniques described in this disclosure may be shared among the various components of video encoder 200. In some examples, a processor may be configured to perform any or all of the techniques described in this disclosure.

The functional components of video encoder 200 may include a partition unit 201, a predication unit 202 which may include a mode select unit 203, a motion estimation unit 204, a motion compensation unit 205 and an intra prediction unit 206, a residual generation unit 207, a transform unit 208, a quantization unit 209, an inverse quantization unit 210, an inverse transform unit 211, a reconstruction unit 212, a buffer 213, and an entropy encoding unit 214.

In other examples, video encoder 200 may include more, fewer, or different functional components. In an example, predication unit 202 may include an intra block copy (IBC) unit. The IBC unit may perform predication in an IBC mode in which at least one reference picture is a picture where the current video block is located.

Furthermore, some components, such as motion estimation unit 204 and motion compensation unit 205 may be highly integrated, but are represented in the example of FIG. 5 separately for purposes of explanation.

Partition unit 201 may partition a picture into one or more video blocks. Video encoder 200 and video decoder 300 may support various video block sizes.

Mode select unit 203 may select one of the coding modes, intra or inter, e.g., based on error results, and provide the resulting intra- or inter-coded block to a residual generation unit 207 to generate residual block data and to a reconstruction unit 212 to reconstruct the encoded block for use as a reference picture. In some example, Mode select unit 203 may select a combination of intra and inter predication (CIIP) mode in which the predication is based on an inter predication signal and an intra predication signal. Mode select unit 203 may also select a resolution for a motion vector (e.g., a sub-pixel or integer pixel precision) for the block in the case of inter-predication.

To perform inter prediction on a current video block, motion estimation unit 204 may generate motion information for the current video block by comparing one or more reference frames from buffer 213 to the current video block. Motion compensation unit 205 may determine a predicted video block for the current video block based on the motion information and decoded samples of pictures from buffer 213 other than the picture associated with the current video block.

Motion estimation unit 204 and motion compensation unit 205 may perform different operations for a current video block, for example, depending on whether the current video block is in an I slice, a P slice, or a B slice.

In some examples, motion estimation unit 204 may perform uni-directional prediction for the current video block, and motion estimation unit 204 may search reference pictures of list 0 or list 1 for a reference video block for the current video block. Motion estimation unit 204 may then generate a reference index that indicates the reference picture in list 0 or list 1 that contains the reference video block and a motion vector that indicates a spatial displacement between the current video block and the reference video block. Motion estimation unit 204 may output the reference index, a prediction direction indicator, and the motion vector as the motion information of the current video block. Motion compensation unit 205 may generate the predicted video block of the current block based on the reference video block indicated by the motion information of the current video block.

In other examples, motion estimation unit 204 may perform bi-directional prediction for the current video block, motion estimation unit 204 may search the reference pictures in list 0 for a reference video block for the current video block and may also search the reference pictures in list 1 for another reference video block for the current video block. Motion estimation unit 204 may then generate reference indexes that indicate the reference pictures in list 0 and list 1 containing the reference video blocks and motion vectors that indicate spatial displacements between the reference video blocks and the current video block. Motion estimation unit 204 may output the reference indexes and the motion vectors of the current video block as the motion information of the current video block. Motion compensation unit 205 may generate the predicted video block of the current video block based on the reference video blocks indicated by the motion information of the current video block.

In some examples, motion estimation unit 204 may output a full set of motion information for decoding processing of a decoder.

In some examples, motion estimation unit 204 may do not output a full set of motion information for the current video. Rather, motion estimation unit 204 may signal the motion information of the current video block with reference to the motion information of another video block. For example, motion estimation unit 204 may determine that the motion information of the current video block is sufficiently similar to the motion information of a neighboring video block.

In one example, motion estimation unit 204 may indicate, in a syntax structure associated with the current video block, a value that indicates to the video decoder 300 that the current video block has the same motion information as another video block.

In another example, motion estimation unit 204 may identify, in a syntax structure associated with the current video block, another video block and a motion vector difference (MVD). The motion vector difference indicates a difference between the motion vector of the current video block and the motion vector of the indicated video block. The video decoder 300 may use the motion vector of the indicated video block and the motion vector difference to determine the motion vector of the current video block.

As discussed above, video encoder 200 may predictively signal the motion vector. Two examples of predictive signaling techniques that may be implemented by video encoder 200 include advanced motion vector predication (AMVP) and merge mode signaling.

Intra prediction unit 206 may perform intra prediction on the current video block. When intra prediction unit 206 performs intra prediction on the current video block, intra prediction unit 206 may generate prediction data for the current video block based on decoded samples of other video blocks in the same picture. The prediction data for the current video block may include a predicted video block and various syntax elements.

Residual generation unit 207 may generate residual data for the current video block by subtracting (e.g., indicated by the minus sign) the predicted video block(s) of the current video block from the current video block. The residual data of the current video block may include residual video blocks that correspond to different sample components of the samples in the current video block.

In other examples, there may be no residual data for the current video block for the current video block, for example in a skip mode, and residual generation unit 207 may not perform the subtracting operation.

Transform processing unit 208 may generate one or more transform coefficient video blocks for the current video block by applying one or more transforms to a residual video block associated with the current video block.

After transform processing unit 208 generates a transform coefficient video block associated with the current video block, quantization unit 209 may quantize the transform coefficient video block associated with the current video block based on one or more quantization parameter (QP) values associated with the current video block.

Inverse quantization unit 210 and inverse transform unit 211 may apply inverse quantization and inverse transforms to the transform coefficient video block, respectively, to reconstruct a residual video block from the transform coefficient video block. Reconstruction unit 212 may add the reconstructed residual video block to corresponding samples from one or more predicted video blocks generated by the predication unit 202 to produce a reconstructed video block associated with the current block for storage in the buffer 213.

After reconstruction unit 212 reconstructs the video block, loop filtering operation may be performed reduce video blocking artifacts in the video block.

Entropy encoding unit 214 may receive data from other functional components of the video encoder 200. When entropy encoding unit 214 receives the data, entropy encoding unit 214 may perform one or more entropy encoding operations to generate entropy encoded data and output a bitstream that includes the entropy encoded data.

FIG. 6 is a block diagram illustrating an example of video decoder 300 which may be video decoder 114 in the system 100 illustrated in FIG. 4 .

The video decoder 300 may be configured to perform any or all of the techniques of this disclosure. In the example of FIG. 6 , the video decoder 300 includes a plurality of functional components. The techniques described in this disclosure may be shared among the various components of the video decoder 300. In some examples, a processor may be configured to perform any or all of the techniques described in this disclosure.

In the example of FIG. 6 , video decoder 300 includes an entropy decoding unit 301, a motion compensation unit 302, an intra prediction unit 303, an inverse quantization unit 304, an inverse transformation unit 305, and a reconstruction unit 306 and a buffer 307. Video decoder 300 may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder 200 (FIG. 5 ).

Entropy decoding unit 301 may retrieve an encoded bitstream. The encoded bitstream may include entropy coded video data (e.g., encoded blocks of video data). Entropy decoding unit 301 may decode the entropy coded video data, and from the entropy decoded video data, motion compensation unit 302 may determine motion information including motion vectors, motion vector precision, reference picture list indexes, and other motion information. Motion compensation unit 302 may, for example, determine such information by performing the AMVP and merge mode.

Motion compensation unit 302 may produce motion compensated blocks, possibly performing interpolation based on interpolation filters. Identifiers for interpolation filters to be used with sub-pixel precision may be included in the syntax elements.

Motion compensation unit 302 may use interpolation filters as used by video encoder 200 during encoding of the video block to calculate interpolated values for sub-integer pixels of a reference block. Motion compensation unit 302 may determine the interpolation filters used by video encoder 200 according to received syntax information and use the interpolation filters to produce predictive blocks.

Motion compensation unit 302 may uses some of the syntax information to determine sizes of blocks used to encode frame(s) and/or slice(s) of the encoded video sequence, partition information that describes how each macroblock of a picture of the encoded video sequence is partitioned, modes indicating how each partition is encoded, one or more reference frames (and reference frame lists) for each inter-encoded block, and other information to decode the encoded video sequence.

Intra prediction unit 303 may use intra prediction modes for example received in the bitstream to form a prediction block from spatially adjacent blocks. Inverse quantization unit 303 inverse quantizes, i.e., de-quantizes, the quantized video block coefficients provided in the bitstream and decoded by entropy decoding unit 301. Inverse transform unit 303 applies an inverse transform.

Reconstruction unit 306 may sum the residual blocks with the corresponding prediction blocks generated by motion compensation unit 202 or intra-prediction unit 303 to form decoded blocks. If desired, a deblocking filter may also be applied to filter the decoded blocks in order to remove blockiness artifacts. The decoded video blocks are then stored in buffer 307, which provides reference blocks for subsequent motion compensation/intra predication and also produces decoded video for presentation on a display device.

A listing of solutions preferred by some embodiments is provided next.

A first set of solutions is provided below. The following solutions show example embodiments of techniques discussed in the previous section (e.g., item 1).

-   -   1. A visual media processing method (e.g., method 700 as shown         in FIG. 3 ), comprising: performing 702 a conversion between a         visual media data and a file storing a bitstream representation         of the visual media data according to a format rule; wherein the         file comprises a track that includes data for a subpicture of         the visual media data; and wherein the format rule specifies a         syntax for the track.     -   2. The method of solution 1, wherein the format rule specifies         that the track covers a rectangular area.     -   3. The method of solution 1, wherein the format rule specifies         that subpictures or slices included in the track are         independently extractable, decodable and presentable.

The following solutions show example embodiments of techniques discussed in the previous section (e.g., items 3, 4).

-   -   4. A visual media processing method, comprising: performing a         conversion between a visual media data and a file storing a         bitstream representation of the visual media data according to a         format rule; wherein the file comprises a first track and/or one         or more subpicture tracks; wherein the format rule specifies a         syntax for the track and/or the one or more subpicture tracks.     -   5. The method of solution 4, wherein the format rule specifies         that the track includes references to the one or more subpicture         tracks.     -   6. The method of solution 4, wherein the format rule disallows         inclusion of access unit level or picture-level non-video coding         layer network abstraction layer units in the one or more         subpicture tracks.     -   7. The method of solution 6, wherein the disallowed units         include a decoding capability information structure, or a         parameter set or operating point information or a header or an         end of stream or an end of picture.     -   8. The method of any of solutions 1-7, wherein the conversion         comprises generating a bitstream representation of the visual         media data and storing the bitstream representation to the file         according to the format rule.     -   9. The method of any of solutions 1-7, wherein the conversion         comprises parsing the file according to the format rule to         recover the visual media data.     -   10. A video decoding apparatus comprising a processor configured         to implement a method recited in one or more of solutions 1 to         9.     -   11. A video encoding apparatus comprising a processor configured         to implement a method recited in one or more of solutions 1 to         9.     -   12. A computer program product having computer code stored         thereon, the code, when executed by a processor, causes the         processor to implement a method recited in any of solutions 1 to         9.     -   13. A computer readable medium on which a bitstream         representation complying to a file format that is generated         according to any of solutions 1 to 9.     -   14. A method, apparatus or system described in the present         document.

A second set of solutions provides example embodiments of techniques discussed in the previous section (e.g., item 1)

-   -   1. A method of processing visual media data (e.g., method 1100         as shown in FIG. 11 ), comprising: performing 1102 a conversion         between visual media data and a visual media file that includes         one or more tracks that store one or more bitstreams of the         visual media data; wherein the visual media data comprises one         or more pictures comprising one or more subpictures or one or         more slices; and wherein the visual media file stores the one or         more tracks according to a format rule; wherein the format rule         specifies that a track that includes a sequence of the one or         more slices or the one or more subpictures covers a rectangular         area of the one or more pictures. FIG. 3 is a flowchart for an         example method of video processing.     -   2. The method of solution 1, wherein the format rule specifies         that the one or more subpictures or one or more slices included         in the track are independently extractable, decodable and         presentable without a presence of another subpicture or another         slice that covers another area different from the rectangular         area.     -   3. The method of solution 1, wherein the format rule specifies         that the one or more subpictures or one or more slices included         in the track are dependent in a motion compensation on another         subpicture or another slice that covers another area different         from the rectangular area.     -   4. The method of solution 1, wherein the format rule specifies         that the one or more slices or the one or more subpictures are         allowed to be not contiguous in a decoding order for a bitstream         stored in the track.     -   5. The method of solution 1, wherein a field of view of a 360         degree video covered by the one or more subpictures that are not         contiguous in the decoding order is represented by the track.     -   6. The method of solution 1, wherein the format rule specifies         that an order of the one or more subpictures or the one or more         slices in each sample of the track is same as an order of the         one or more subpictures or the one or more slices in a bitstream         stored in the track.     -   7. The method of solution 1, wherein the format rule further         specifies whether to include an indication indicative of whether         a decoding order of the one or more subpictures or the one or         more slices in each sample of a track is contiguous in a         bitstream stored in the track.     -   8. The method of solution 7, wherein the indication is included         in a base track sample entry description of the track.     -   9. The method of solution 7, wherein the format rule further         specifies to, in response to an absence of the indication,         disallow the one or more subpictures or the one or more slices         in the track to be merged with another subpicture or another         slice of another track.     -   10. The method of solution 7, wherein the indication is included         in a network abstraction layer (NAL) configuration box.     -   11. The method of solution 7, wherein the indication equal to 1         indicates that NAL units in each sample of the track is         contiguous in the decoding order of the bitstream and a base         track that references the track with a track reference refers to         other tracks with the track reference.     -   12. The method of solution 7, wherein the indication equal to 0         indicates that NAL units in each sample of the track is allowed         to be or not to be contiguous in the decoding order of the         bitstream and a base track that references the track with a         track reference is allowed not to refer to other tracks with the         track reference.     -   13. The method of any one of solutions 1-12, wherein the visual         media data is processed by a versatile video coding (VVC), and         the one or more tracks are VVC tracks.     -   14. The method of any one of solutions 1-13, wherein the         conversion comprises generating the visual media file and         storing the one or more bitstreams to the visual media file         according to the format rule.     -   15. The method of any one of solutions 1-13, wherein the         conversion comprises parsing the visual media file according to         the format rule to reconstruct the one or more bitstream.     -   16. An apparatus of processing visual media data, comprising a         processor configured to implement a method comprising:         performing a conversion between visual media data and a visual         media file that includes one or more tracks that store one or         more bitstreams of the visual media data; wherein the visual         media data comprises one or more pictures comprising one or more         subpictures or one or more slices; and wherein the visual media         file stores the one or more tracks according to a format rule;         wherein the format rule specifies that a track that includes a         sequence of the one or more slices or the one or more         subpictures covers a rectangular area of the one or more         pictures.     -   17. The apparatus of solution 16, wherein the format rule         specifies whether to include an indication indicative of whether         a decoding order of the one or more subpictures or the one or         more slices in each sample of a track is contiguous in a         bitstream stored in the track.     -   18. A non-transitory computer-readable recording medium storing         instructions that cause a processor to: perform a conversion         between visual media data and a visual media file that includes         one or more tracks that store one or more bitstreams of the         visual media data; wherein the visual media data comprises one         or more pictures comprising one or more subpictures or one or         more slices; and wherein the visual media file stores the one or         more tracks according to a format rule; wherein the format rule         specifies that a track that includes a sequence of the one or         more slices or the one or more subpictures covers a rectangular         area of the one or more pictures.     -   19. The non-transitory computer-readable recording medium of         solution 18, wherein the format rule specifies whether to         include an indication indicative of whether a decoding order of         the one or more subpictures or the one or more slices in each         sample of a track is contiguous in a bitstream stored in the         track.     -   20. A non-transitory computer-readable recording medium storing         a bitstream which is generated by a method performed by a video         processing apparatus, wherein the method comprises: generating a         visual media file that includes one or more tracks that store         one or more bitstreams of visual media data; wherein the visual         media data comprises one or more pictures comprising one or more         subpictures or one or more slices; and wherein the visual media         file stores the one or more tracks according to a format rule;         wherein the format rule specifies that a track that includes a         sequence of the one or more slices or the one or more         subpictures covers a rectangular area of the one or more         pictures.     -   21. The non-transitory computer-readable recording medium of         solution 18, wherein the format rule specifies whether to         include an indication indicative of whether a decoding order of         the one or more subpictures or the one or more slices in each         sample of a track is contiguous in a bitstream stored in the         track.     -   22. A video processing apparatus comprising a processor         configured to implement a method recited in any one or more of         solutions 1 to 15.     -   23. A method of storing visual media data to a file including         one or more bitstreams, the method comprising a method recited         in any one of solutions 1 to 15, and further including storing         the bitstream to a non-transitory computer-readable recording         medium.     -   24. A computer readable medium storing program code that, when         executed, causes a processor to implement a method recited in         any one or more of solutions 1 to 15.     -   25. A computer readable medium that stores a bitstream generated         according to any of the above described methods.     -   26. A video processing apparatus for storing a bitstream,         wherein the video processing apparatus is configured to         implement a method recited in any one or more of solutions 1 to         15.     -   27. A computer readable medium on which a bitstream         representation complying to a file format that is generated         according to any of solutions 1 to 15.     -   28. A method, apparatus or system described in the present         document.

A third set of solutions show example embodiments of techniques discussed in the previous section (e.g., items 3, 5, 6, 7, and 10)

-   -   1. A method of processing visual media data (e.g., method 1200         as shown in FIG. 12 ), comprising: performing 1202 a conversion         between visual media data and a visual media file that includes         one or more tracks that store one or more bitstreams of the         visual media data according to a format rule; wherein the visual         media file includes a base track that references one or more         subpicture tracks that store coded information for one or more         subpictures of the visual media data, and wherein the format         rule specifies a process used to reconstruct a video unit from a         sample in the base track and the one or more subpicture tracks.     -   2. The method of solution 1, wherein the format rule specifies         that the base track includes a subpicture track reference to         refer to the one or more subpicture tracks and an order of the         one or more subpicture tracks referenced in the subpicture track         reference indicates an order of samples of the one or more         subpicture tracks in the video unit reconstructed from the one         or more subpicture tracks.     -   3. The method of solution 1, wherein the format rule further         specifies that each subpicture track reference has an index         referring to either a track identification of a subpicture track         or a track group identification of a group of subpicture tracks.     -   4. The method of solution 1, wherein the format rule specifies         that a subpicture order sample group is optional for the base         track.     -   5. The method of solution 4, wherein the format rule further         specifies that, in case that the subpicture order sample group         is absent from the base track, then a subpicture track reference         is used in determining an order of the one or more subpicture         tracks referenced in the base track.     -   6. The method of solution 4, wherein the format rule further         specifies to remove a use of the subpicture order sample group         and to remove a description of a parameter set rewriting process         based on the subpicture order sample group.     -   7. The method of solution 4, wherein the format rule further         specifies to remove a specification of the subpicture order         sample group.     -   8. The method of any one of solutions 1-7, wherein the visual         media data is processed by a versatile video coding (VVC), and         the one or more tracks are VVC tracks.     -   9. The method of any one of solutions 1-8, wherein the         conversion comprises generating the visual media file and         storing the one or more bitstreams to the visual media file         according to the format rule.     -   10. The method of any one of solutions 1-8, wherein the         conversion comprises parsing the visual media file according to         the format rule to reconstruct the one or more bitstreams.     -   11. An apparatus of processing visual media data, comprising a         processor configured to implement a method comprising:         performing a conversion between visual media data and a visual         media file that includes one or more tracks that store one or         more bitstreams of the visual media data according to a format         rule; wherein the visual media file includes a base track that         references one or more subpicture tracks that store coded         information for one or more subpictures of the visual media         data, and wherein the format rule specifies a process used to         reconstruct a video unit from a sample in the base track and the         one or more subpicture tracks.     -   12. The apparatus of solution 11, wherein the format rule         specifies that the base track includes a subpicture track         reference to refer to the one or more subpicture tracks and an         order of the one or more subpicture tracks referenced in the         subpicture track reference indicates an order of samples of the         one or more subpicture tracks in the video unit reconstructed         from the one or more subpicture tracks.     -   13. The apparatus of solution 11, wherein the format rule         further specifies that each subpicture track reference has an         index referring to either a track identification of a subpicture         track or a track group identification of a group of subpicture         tracks.     -   14. The apparatus of solution 11, wherein the format rule         specifies that a subpicture order sample group is optional for         the base track.     -   15. The apparatus of solution 14, wherein the format rule         further specifies that, in case that the subpicture order sample         group is absent from the base track, then a subpicture track         reference is used in determining an order of the one or more         subpicture tracks referenced in the base track.     -   16. The apparatus of solution 14, wherein the format rule         further specifies to remove a use of the subpicture order sample         group and to remove a description of a parameter set rewriting         process based on the subpicture order sample group.     -   17. The apparatus of solution 14, wherein the format rule         further specifies to remove a specification of the subpicture         order sample group.     -   18. A non-transitory computer-readable recording medium storing         instructions that cause a processor to: perform a conversion         between visual media data and a visual media file that includes         one or more tracks that store one or more bitstreams of the         visual media data according to a format rule; wherein the visual         media file includes a base track that references one or more         subpicture tracks that store coded information for one or more         subpictures of the visual media data, and wherein the format         rule specifies a process used to reconstruct a video unit from a         sample in the base track and the one or more subpicture tracks.     -   19. The non-transitory computer-readable recording medium of         solution 18, wherein the format rule specifies that the base         track includes a subpicture track reference to refer to the one         or more subpicture tracks and an order of the one or more         subpicture tracks referenced in the subpicture track reference         indicates an order of samples of the one or more subpicture         tracks in the video unit reconstructed from the one or more         subpicture tracks.     -   20. A non-transitory computer-readable recording medium storing         a bitstream which is generated by a method performed by a video         processing apparatus, wherein the method comprises: generating a         visual media file that includes one or more tracks that store         one or more bitstreams of visual media data according to a         format rule; wherein the visual media file includes a base track         that references one or more subpicture tracks that store coded         information for one or more subpictures of the visual media         data, and wherein the format rule specifies a process used to         reconstruct a video unit from a sample in the base track and the         one or more subpicture tracks.     -   21. A video processing apparatus comprising a processor         configured to implement a method recited in any one or more of         solutions 1 to 10.     -   22. A method of storing visual media data to a file including         one or more bitstreams, the method comprising a method recited         in any one of solutions 1 to 10, and further including storing         the bitstream to a non-transitory computer-readable recording         medium.     -   23. A computer readable medium storing program code that, when         executed, causes a processor to implement a method recited in         any one or more of solutions 1 to 10.     -   24. A computer readable medium that stores a bitstream generated         according to any of the above described methods.     -   25. A video processing apparatus for storing a bitstream,         wherein the video processing apparatus is configured to         implement a method recited in any one or more of solutions 1 to         10.     -   26. A computer readable medium on which a bitstream         representation complying to a file format that is generated         according to any of solutions 1 to 10.     -   27. A method, apparatus or system described in the present         document.

In the example solutions, the visual media data corresponds to video or images. In the solutions described herein, an encoder may conform to the format rule by producing a coded representation according to the format rule. In the solutions described herein, a decoder may use the format rule to parse syntax elements in the coded representation with the knowledge of presence and absence of syntax elements according to the format rule to produce decoded video. In the solutions above, the visual media data corresponds to video or images.

In the present document, the term “video processing” may refer to video encoding, video decoding, video compression or video decompression. For example, video compression algorithms may be applied during conversion from pixel representation of a video to a corresponding bitstream representation or vice versa. The bitstream representation of a current video block may, for example, correspond to bits that are either co-located or spread in different places within the bitstream, as is defined by the syntax. For example, a macroblock may be encoded in terms of transformed and coded error residual values and also using bits in headers and other fields in the bitstream. Furthermore, during conversion, a decoder may parse a bitstream with the knowledge that some fields may be present, or absent, based on the determination, as is described in the above solutions. Similarly, an encoder may determine that certain syntax fields are or are not to be included and generate the coded representation accordingly by including or excluding the syntax fields from the coded representation.

The disclosed and other solutions, examples, embodiments, modules and the functional operations described in this document can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this document and their structural equivalents, or in combinations of one or more of them. The disclosed and other embodiments can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a computer readable medium for execution by, or to control the operation of, data processing apparatus. The computer readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more them. The term “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. A propagated signal is an artificially generated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to suitable receiver apparatus.

A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

The processes and logic flows described in this document can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random-access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices. Computer readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

While this patent document contains many specifics, these should not be construed as limitations on the scope of any subject matter or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular techniques. Certain features that are described in this patent document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system components in the embodiments described in this patent document should not be understood as requiring such separation in all embodiments.

Only a few implementations and examples are described and other implementations, enhancements and variations can be made based on what is described and illustrated in this patent document. 

The invention claimed is:
 1. A method of processing visual media data, comprising: performing a conversion between visual media data and a visual media file that includes one or more tracks that store one or more bitstreams of the visual media data, wherein the visual media data comprises one or more pictures comprising one or more subpictures or one or more slices; wherein the visual media file stores the one or more tracks according to a format rule, and the visual media file includes a base track that references one or more subpicture tracks that store coded information for one or more subpictures of the visual media data; wherein the format rule specifies that a track includes a sequence of the one or more slices or the one or more subpictures and the one or more slices or the one or more subpictures cover a rectangular area of the one or more pictures, and wherein the format rule specifies that the base track includes a subpicture track reference to refer to the one or more subpicture tracks and an order of the one or more subpicture tracks referenced in the subpicture track reference indicates an order of samples of the one or more subpicture tracks in a video unit reconstructed from the one or more subpicture tracks.
 2. The method of claim 1, wherein the format rule specifies that the one or more subpictures or one or more slices included in the track are independently extractable, decodable and presentable without a presence of another subpicture or another slice that covers another area different from the rectangular area.
 3. The method of claim 1, wherein the format rule specifies that the one or more subpictures or one or more slices included in the track are dependent in a motion compensation on another subpicture or another slice that covers another area different from the rectangular area.
 4. The method of claim 1, wherein a field of view of a 360 degree video covered by the one or more subpictures that are not contiguous in a decoding order is represented by the track.
 5. The method of claim 1, wherein the format rule specifies that an order of subpictures or slices in each sample of the track is same as an order of subpictures or slices in a bitstream stored in the track.
 6. The method of claim 1, wherein the format rule further specifies whether to include an indication indicative of whether a decoding order of the one or more subpictures or the one or more slices in each sample of a track is contiguous in a bitstream stored in the track.
 7. The method of claim 6, wherein the indication is included in a base track sample entry description of the track.
 8. The method of claim 6, wherein the format rule further specifies to, in response to an absence of the indication, disallow the one or more subpictures or the one or more slices in the track to be merged with another subpicture or another slice of another track.
 9. The method of claim 6, wherein the indication is included in a network abstraction layer (NAL) configuration box.
 10. The method of claim 6, wherein the indication equal to 1 indicates that NAL units in each sample of the track is contiguous in the decoding order of the bitstream and a base track that references the track with a track reference refers to other tracks with the track reference.
 11. The method of claim 6, wherein the indication equal to 0 indicates that NAL units in each sample of the track is allowed to be or not to be contiguous in the decoding order of the bitstream and a base track that references the track with a track reference is allowed not to refer to other tracks with the track reference.
 12. The method of claim 1, wherein the visual media data is processed by a versatile video coding (VVC), and the one or more tracks are VVC tracks.
 13. The method of claim 1, wherein the conversion comprises generating the visual media file and storing the one or more bitstreams to the visual media file according to the format rule.
 14. The method of claim 1, wherein the conversion comprises parsing the visual media file according to the format rule to reconstruct the one or more bitstreams.
 15. An apparatus of processing visual media data, comprising a processor configured to implement a method comprising: performing a conversion between visual media data and a visual media file that includes one or more tracks that store one or more bitstreams of the visual media data; wherein the visual media data comprises one or more pictures comprising one or more subpictures or one or more slices; wherein the visual media file stores the one or more tracks according to a format rule, and the visual media file includes a base track that references one or more subpicture tracks that store coded information for one or more subpictures of the visual media data; wherein the format rule specifies that a track includes a sequence of the one or more slices or the one or more subpictures and the one or more slices or the one or more subpictures cover a rectangular area of the one or more pictures, and wherein the format rule specifies that the base track includes a subpicture track reference to refer to the one or more subpicture tracks and an order of the one or more subpicture tracks referenced in the subpicture track reference indicates an order of samples of the one or more subpicture tracks in a video unit reconstructed from the one or more subpicture tracks.
 16. The apparatus of claim 15, wherein the format rule specifies whether to include an indication indicative of whether a decoding order of the one or more subpictures or the one or more slices in each sample of a track is contiguous in a bitstream stored in the track.
 17. A non-transitory computer-readable recording medium storing instructions that cause a processor to: perform a conversion between visual media data and a visual media file that includes one or more tracks that store one or more bitstreams of the visual media data; wherein the visual media data comprises one or more pictures comprising one or more subpictures or one or more slices; wherein the visual media file stores the one or more tracks according to a format rule, and the visual media file includes a base track that references one or more subpicture tracks that store coded information for one or more subpictures of the visual media data; wherein the format rule specifies that a track includes a sequence of the one or more slices or the one or more subpictures and the one or more slices or the one or more subpictures cover a rectangular area of the one or more pictures, and wherein the format rule specifies that the base track includes a subpicture track reference to refer to the one or more subpicture tracks and an order of the one or more subpicture tracks referenced in the subpicture track reference indicates an order of samples of the one or more subpicture tracks in a video unit reconstructed from the one or more subpicture tracks.
 18. The non-transitory computer-readable recording medium of claim 17, wherein the format rule specifies whether to include an indication indicative of whether a decoding order of the one or more subpictures or the one or more slices in each sample of a track is contiguous in a bitstream stored in the track.
 19. A non-transitory computer-readable recording medium storing a bitstream which is generated by a method performed by a video processing apparatus, wherein the method comprises: generating a visual media file that includes one or more tracks that store one or more bitstreams of visual media data; wherein the visual media data comprises one or more pictures comprising one or more subpictures or one or more slices; wherein the visual media file stores the one or more tracks according to a format rule, and the visual media file includes a base track that references one or more subpicture tracks that store coded information for one or more subpictures of the visual media data; wherein the format rule specifies that a track includes a sequence of the one or more slices or the one or more subpictures and the one or more slices or the one or more subpictures cover a rectangular area of the one or more pictures, and wherein the format rule specifies that the base track includes a subpicture track reference to refer to the one or more subpicture tracks and an order of the one or more subpicture tracks referenced in the subpicture track reference indicates an order of samples of the one or more subpicture tracks in a video unit reconstructed from the one or more subpicture tracks.
 20. The method of claim 1, wherein the format rule specifies that the one or more slices or the one or more subpictures are allowed to be not contiguous in a decoding order for a bitstream stored in the track. 